Thomas Young, born in 1773 was the oldest of his ten brothers and sisters. He started early on his studies, was acquainted with multiple languages, and attended school to learn medicine. Soon after, he moved schools and got his degree as doctor of physics. Young became a professor of natural philosophy and physics at the Royal Institution in Great Britain. He held many positions in his life including the foreign secretary of the Royal Society, a physician at St. George’s Hospital, secretary to the Board of Longitude and a superintendent for the HM Nautical Almanac Office. Thomas Young died in London in 1829. [1]
Works and Theories
He was well known for some of his works and praised among physicists for his theories. He and another scientist, in 1807, were theorizing about color vision and found a defect that we know as astigmatismThomas Young is credited with suggesting that the eye has three different kinds of color receptors, corresponding roughly with the red, green, and blue primary colors. Hermann von Helmholtz put more definition on this theory and it is sometimes called the Young-Helmholtz theory. One of his most prominent theories was the theory that light was actually waves and not particles as previous physicist like Isaac Newton had theorized.[2]
Young researched and worked on this problem. In the end, he came up with two ways to show his theory. In the paper, Experiments and Calculations Relative to Physical Optics, 1803, Young describes his experiment that was to support his idea that light comes in waves. Thomas placed a narrow card in a beam of light from a window and observed the fringes of color that appeared in the shadow and to the sides of the card. Young observed that placing another card before or after the narrow strip to prevent light from the beam from striking one of its edges caused the fringes to disappear.
Other well known physicists
Isaac Newton was a physicist who lived from 1643 to 1727. He was well known for his work on universal gravitation and the three laws of motion. Modern physicist and scientists rank Newton next to Albert Einstein. Sir Isaac Newton proposed the corpuscular theory of light, and states that light is made up of small particles. This was unable to explain interference and diffraction and therefore Young’s theory of waves was more likely to be true. Newton’s law was soon replaced by the wave-particle duality.
Wave particle duality is a concept of quantum mechanics and states that matter exists in particles and waves. Two theories were presented, one by Christiaan Huygens and one by Isaac Newton. Huygens thought that light consisted of waves and Newton argued that it consisted of particles. Christiaan Huygens came up with a theory that was later named “Huygens principle.” He believed light was a series of waves vibrating perpendicular to the direction light travels. It formulated a way to visualize the way the waves traveled. Many scientists worked on this problem, but Young was one of the only succeeding scientists that could show it through the data of an experiment with the light, that could also be repeated to check accuracy. This experiment was known as Young’s Interference experiment.[3]
Young's Experiment
Light waves consist of many different types and kinds, the difference being the lengths which make the colors. They can be seen as red, orange, yellow, green, blue, indigo, and violet. Waves are visible only in color, and when combined we get white light. While the sun is the natural source of visible light, light bulbs act as a substitute when the sunlight can’t be seen. Wavelengths can be characterized by wavelength and by the frequency of the wave. Wavelength is the distance between one crest and the next. Frequency is how many waves pass a point in one second.[4] Although for many years scientists explained the mystery of light as just an imperfect understanding of atoms and interaction of light and the ideas were vague, Einstein found a simple solution. Today we have the cameras and electronics to make it easier. Scientists now use cameras to find evidence of particles in light. The camera detects smaller amounts of light and have a different view than normal. Einstein concluded in a paper in 1905, that the energy of lights comes in chunks rather than smoothly. We now think of these chunks as particles of light.
To settle this dispute for his own gain, Young came up with the double-slit experiment. Young allowed sunlight to fall on a pinhole punched in a screen, creating a point source of light by diffraction. The light then fell upon a second screen through which two pinholes with a small separation had been punched. The overlapping region showed a striped pattern alternating light and darkness. It has been found convenient to replace the pinholes with narrow slits and use a monochromatic light source and can also be enhanced by using a large number of equally spaced slits to form a diffraction grating. Monochromatic is something with only one color, so the monochromatic light is a light with only one wavelength or color.
Diffraction is when a wave encounters an obstacle. Light diffraction occurs when a light wave passes through an opening or slit about the same size or smaller than the light wave length. A good example of this by sunlight is looking at the clouds. The “silver lining” around the clouds is the sunlight diffraction. The sunlight does not shine through the clouds as bright, but around them. Color is also produced in the clouds when you have diffraction off of the rain droplets. The definition of diffraction grating is a plate of glass or metal ruled with very close parallel lines, producing a spectrum by diffraction and interference of light. Interference, different from diffraction, is when two waves interact. There are two types, constructive interference and destructive interference. Constructive is when a wave’s amplitude is increased. Two waves traveling in opposite directions, when the waves meet the amplitudes are added together. Once it passes though, it goes back to normal. Destructive is when the crest meets the trough. This cancels out the other wave, and again becomes normal when it passes.
To recreate this experiment you will need a light source, a piece of cardboard with a slit cut vertically into the middle, and a blank wall as to see the results. The light source need to only have one wavelength and the cardboard needs to be big enough to have 2 slits about 5 mm wide about 2 cm apart and 0.3 m long each. The light radiates outward as it travels, so you do not end up with two small lines, but with two lines spread out with more concentrated light in the middle, and fuzzier edges. The pattern is the same with any amount of slits, just a different number of lines.
Sunlight is all different wavelengths, almost like white light. You can tell when it is tested through a prism. The difference between a laser and a flashlight is that flashlights put out all kinds of waves, while lasers are monochromatic. LED lights can be seen in many different colors, most however with the blue or white light. For this experiment you would not want to use the white light types. White light consists of a mix of all light wavelengths and since this experiment only works correctly with a monochromatic light the results may be off.
My recreation of the experiment
Planned Procedure:
My planned procedure is to use the top of a shoe box for the cardboard, as it isn’t corrugated cardboard. I chose a red laser, an LED light, and a regular flashlight. These will give a contrast in the light waves. It will show why white light differs from the red light or the blue. Set the cardboard a couple of inches from a blank wall in a pitch black room and try each light source separately. Multiple trials of each and also each used not only with one slit, but with two slits and with holes. Taking videos of each as experimented and compared at the end of the experiment.
Materials: red laser flashlight led light cardboard with a single slit and a double slit camera or recording device
Procedure: I used not only a red laser, but an led light and a regular flashlight and recorded the evidence with pictures and video to compare. As the research shows it should only work with the red laser because of what kind of light it is and yet the red laser is the one that cannot be seen in the pictures. I used the lid of a shoe box to cut the slits in and set it in a dark room. With the red laser not only was the red laser not strong enough, it also didn't reflect in the pictures as it was on the wall.
Table of Contents
Young's Double Slit Experiment
Life of a physicist
Thomas Young, born in 1773 was the oldest of his ten brothers and sisters. He started early on his studies, was acquainted with multiple languages, and attended school to learn medicine. Soon after, he moved schools and got his degree as doctor of physics. Young became a professor of natural philosophy and physics at the Royal Institution in Great Britain. He held many positions in his life including the foreign secretary of the Royal Society, a physician at St. George’s Hospital, secretary to the Board of Longitude and a superintendent for the HM Nautical Almanac Office. Thomas Young died in London in 1829. [1]
Works and Theories
He was well known for some of his works and praised among physicists for his theories. He and another scientist, in 1807, were theorizing about color vision and found a defect that we know as astigmatismThomas Young is credited with suggesting that the eye has three different kinds of color receptors, corresponding roughly with the red, green, and blue primary colors. Hermann von Helmholtz put more definition on this theory and it is sometimes called the Young-Helmholtz theory. One of his most prominent theories was the theory that light was actually waves and not particles as previous physicist like Isaac Newton had theorized. [2]Young researched and worked on this problem. In the end, he came up with two ways to show his theory. In the paper, Experiments and Calculations Relative to Physical Optics, 1803, Young describes his experiment that was to support his idea that light comes in waves. Thomas placed a narrow card in a beam of light from a window and observed the fringes of color that appeared in the shadow and to the sides of the card. Young observed that placing another card before or after the narrow strip to prevent light from the beam from striking one of its edges caused the fringes to disappear.
Other well known physicists
Isaac Newton was a physicist who lived from 1643 to 1727. He was well known for his work on universal gravitation and the three laws of motion. Modern physicist and scientists rank Newton next to Albert Einstein. Sir Isaac Newton proposed the corpuscular theory of light, and states that light is made up of small particles. This was unable to explain interference and diffraction and therefore Young’s theory of waves was more likely to be true. Newton’s law was soon replaced by the wave-particle duality.Wave particle duality is a concept of quantum mechanics and states that matter exists in particles and waves. Two theories were presented, one by Christiaan Huygens and one by Isaac Newton. Huygens thought that light consisted of waves and Newton argued that it consisted of particles. Christiaan Huygens came up with a theory that was later named “Huygens principle.” He believed light was a series of waves vibrating perpendicular to the direction light travels. It formulated a way to visualize the way the waves traveled. Many scientists worked on this problem, but Young was one of the only succeeding scientists that could show it through the data of an experiment with the light, that could also be repeated to check accuracy. This experiment was known as Young’s Interference experiment.[3]
Young's Experiment
Light waves consist of many different types and kinds, the difference being the lengths which make the colors. They can be seen as red, orange, yellow, green, blue, indigo, and violet. Waves are visible only in color, and when combined we get white light. While the sun is the natural source of visible light, light bulbs act as a substitute when the sunlight can’t be seen. Wavelengths can be characterized by wavelength and by the frequency of the wave. Wavelength is the distance between one crest and the next. Frequency is how many waves pass a point in one second. [4]Although for many years scientists explained the mystery of light as just an imperfect understanding of atoms and interaction of light and the ideas were vague, Einstein found a simple solution. Today we have the cameras and electronics to make it easier. Scientists now use cameras to find evidence of particles in light. The camera detects smaller amounts of light and have a different view than normal. Einstein concluded in a paper in 1905, that the energy of lights comes in chunks rather than smoothly. We now think of these chunks as particles of light.
To settle this dispute for his own gain, Young came up with the double-slit experiment. Young allowed sunlight to fall on a pinhole punched in a screen, creating a point source of light by diffraction. The light then fell upon a second screen through which two pinholes with a small separation had been punched. The overlapping region showed a striped pattern alternating light and darkness. It has been found convenient to replace the pinholes with narrow slits and use a monochromatic light source and can also be enhanced by using a large number of equally spaced slits to form a diffraction grating. Monochromatic is something with only one color, so the monochromatic light is a light with only one wavelength or color.
Diffraction is when a wave encounters an obstacle. Light diffraction occurs when a light wave passes through an opening or slit about the same size or smaller than the light wave length. A good example of this by sunlight is looking at the clouds. The “silver lining” around the clouds is the sunlight diffraction. The sunlight does not shine through the clouds as bright, but around them. Color is also produced in the clouds when you have diffraction off of the rain droplets. The definition of diffraction grating is a plate of glass or metal ruled with very close parallel lines, producing a spectrum by diffraction and interference of light.
Interference, different from diffraction, is when two waves interact. There are two types, constructive interference and destructive interference. Constructive is when a wave’s amplitude is increased. Two waves traveling in opposite directions, when the waves meet the amplitudes are added together. Once it passes though, it goes back to normal. Destructive is when the crest meets the trough. This cancels out the other wave, and again becomes normal when it passes.
[5]
To recreate this experiment you will need a light source, a piece of cardboard with a slit cut vertically into the middle, and a blank wall as to see the results. The light source need to only have one wavelength and the cardboard needs to be big enough to have 2 slits about 5 mm wide about 2 cm apart and 0.3 m long each. The light radiates outward as it travels, so you do not end up with two small lines, but with two lines spread out with more concentrated light in the middle, and fuzzier edges. The pattern is the same with any amount of slits, just a different number of lines.
Sunlight is all different wavelengths, almost like white light. You can tell when it is tested through a prism. The difference between a laser and a flashlight is that flashlights put out all kinds of waves, while lasers are monochromatic. LED lights can be seen in many different colors, most however with the blue or white light. For this experiment you would not want to use the white light types. White light consists of a mix of all light wavelengths and since this experiment only works correctly with a monochromatic light the results may be off.
My recreation of the experiment
Planned Procedure:
My planned procedure is to use the top of a shoe box for the cardboard, as it isn’t corrugated cardboard. I chose a red laser, an LED light, and a regular flashlight. These will give a contrast in the light waves. It will show why white light differs from the red light or the blue. Set the cardboard a couple of inches from a blank wall in a pitch black room and try each light source separately. Multiple trials of each and also each used not only with one slit, but with two slits and with holes. Taking videos of each as experimented and compared at the end of the experiment.Materials:
red laser
flashlight
led light
cardboard with a single slit and a double slit
camera or recording device
Procedure:
I used not only a red laser, but an led light and a regular flashlight and recorded the evidence with pictures and video to compare.
As the research shows it should only work with the red laser because of what kind of light it is and yet the red laser is the one that cannot be seen in the pictures.
I used the lid of a shoe box to cut the slits in and set it in a dark room. With the red laser not only was the red laser not strong enough, it also didn't reflect in the pictures as it was on the wall.
Pictures included in the presentation
Physics-Double slit experiment on Prezi
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